Circuit board drier

ABSTRACT

In an apparatus for drying circuit boards, two sets of rollers convey a circuit board past a set of air knives of novel configuration. Each air knife comprises a pair of planar blade members converging to form adjacent their apex an elongate orifice having a width on the order of 0.085 inches. A deflector lip projects from one edge of the orifice. Air forced through the orifice forms an air knife edge having an anemometer static pressure of greater than 10 inches of water, providing exceptionally quiet, highly effective drying of the board. In some embodiments, a plurality of upper and lower horizontally disposed guidewires facilitate drying of thin, flexible boards.

United States Patent l 13,579,853

[72] Inventor Joseph J. Martino 2.729.324 7/1956 Howdle 198/127UX 7013E1 Prauo Circle, Buena Park, Calif. 2,864,406 12/ 1958 Schewel 239/521X90620 3.071.365 1/1963 Faeber 34/160X [21] Appl. No. 781,566 3,319,3545/1967 Hering 34/160X {22] Filed Dec. 5, 1968 3,398,466 8/1968 Brown34/160 [45] Patented May 25, 1971 3,429,057 2/1969 Thygeson 34/160Primary Examiner-Edward J. Michael Attorney-Hinderstein and Silber [54]CIRCUIT BOARD DRIER ll ClmmsADrawmg Flgs. ABSTRACT: In an apparatus fordrying circuit boards, two [52] 11.8. C1 34/218, Sets of rollers conveya Circuit board past a set f air knives of 34/160 239/521 novelconfiguration. Each air knife comprises a pair of planar blade membersconverging to form adjacent their apex an [501 new of 34/218 elongateorifice having a width on the order of 0.085 inches. A 160, 148;198/127; 239/597, 598, 52 deflector lip projects from one edge of theorifice. Air forced throu h the orifice forms an air knife ed e havin an[56] References Cited anem meter static pressure of greater than 10ifches of w ater, UNITED STATES PATENTS providing exceptionally quiet,highly efi'ective drying of the 1,320,108 10/1919 Werlin 239/523 board.In some embodiments, a plurality of upper and lower 2,192,657 3/ 1940Werther 239/523X horizontally disposed guidewires facilitate drying ofthin, flexi- 1,759,804 5/1930 Pieron ble boards.

PATENTED "M25 I97! SHEET 1 BF 3 INVENTOR.

JOSEPH J. MARTINO Hwwtwg s} $414.1,

ATTORNEYS PATENTEU W25 |97l SHEET 2 BF 3 INVENTOR.

JOSEPH J. MARTINO SUN,

AT TORNEYS PATENTED W25 IQYI SHEET 3 BF 3 ul-4st; q sash ATTORNEYSCIRCUIT BOARD DRIER BACKGROUND or THE INVENTION 1. Field of theInvention The present invention relates to an apparatus for dryingcircuit boards, and, more particularly, to a circuit board drieremploying an air knife having a thin, elongate orifice and a deflectorlip extending from one edge thereof.

2. Description of the Prior Art In virtually all present day electronicequipment, the various electronic components, be they individualtransistors, resistors and capacitors or complex microelectronic chips,are interconnected by means of printed circuit boards. These circuitboards typically comprise an insulative substrate of phenolic, glassimpregnated epoxy or the like, both surfaces of which are provided withthin, planar interconnections of a conductive material such as copper.Often, through-plated holes interconnect the circuitry on the two sidesof the board.

Formation of such circuit boards generally begins with the drilling ofthrough holes, followed by electroless and electrolytic plating of theentire board with copper or other conductive material. This copper layerthen is coated with a photosensitive resist material such as Kodak KPR,the resist then being exposed to light through a photographic maskcontaining an image of the desired circuit pattern. When the exposedphotoresist is developed, the areas defining the desired circuit patternpolymerize, while the remaining areas may be washed with an appropriatesolvent. The thus developed pattern serves as a mask for an acid whichpreferentially etches away the copper from regions not covered withphotoresist. The etchant does not attack the insulative substrate. Whenthe etching has been completed, theresidual polymerized photoresist isremoved with an appropriate stripper, leaving a circuit board having aconductive pattern on one or both surfaces of the insulative substrate.

It will be appreciated that at several stages of fabrication suchcircuit boards must be immersed in various liquids such as solvents,photoresists, etchants and the like; the boards also must be washed inwater at certain times. To insure defectfree boards, the boards must bedried completely after several of these fabrication steps.

For example, after the insulative substrate has been drilled anddeburred, but before it has been metal-plated, the board must becompletely dry to insure that electroless copper deposited on thesurface and through-holes will form a continuous coating, free fromvoids which may result in intermittent or open electrical circuits.Similarly, after the plated copper has been etched, the board must becompletely dry before the photoresist is removed. If water is present,it tends to cause coagulation of the photoresist stripper, significantlydecreasing its effectiveness. Finally, it is important that the finishedboard be dried completely. This insures the absence of residual waterwhich nright cause tarnishing or oxidation of the copperinterconnections during storage of the board between the time it isfabricated and the time when components are mounted thereon.

Prior art circuit board driers have suffered from a number ofdisadvantages. For example, one commonly used drier is fashioned in theform of a two-pronged yoke or fork. The circuit board to be dried isplaced between the prongs and air then is directed through the prongsedgewise over the board. Such an apparatus is clumsy in that each boardmust be placed on the drier individually. More important, the airflowfrom opposite edges of the board is nonuniform over the entire surface,leading to nonuniform drying of the board. Further, only cal is theapparatus in which a board was conveyed under one or more cylinders eachprovided with a pluiality ofholes. Air i air was random directed, withair blasts fromseveral of the holes often causing splashing of the wateronto other parts of the board, thereby making more acute the wettingproblem. Typically, it was necessary to pass the board under the drierseveral times to accomplish even reasonable drying.

In other prior art driers, the circuit board was conveyed past acylinder having a narrow slot in it through which a bladelike flow ofair was directed toward the board. However, such prior art blades hadseveral disadvantages. First, it was difficult to direct the flow of airthrough such openings, and when using air of even reasonably highpressure, these slotted cylinders generated such an excessively highnoise level as to make them commercially unacceptable.

Another shortcoming indigenous to prior art conveyor-type circuit boarddriers was that very thin, flexible circuit boards could not be dried bythese machines. Such circuit boards, typically on the order of 0.002inch thick, are extremely flexible, and when run through prior artconveyor-type. driers tended to be blown upward or downward into theconveyor or air knife mechanism, fouling the drier apparatus rather thandrying the board.

These and other shortcomings of the prior art are overcome by using theinventive circuit board drier wherein a unique air knife is employedpermitting quiet, effective drying of a circuit board conveyed past theair knife. A unique conveyor arrangement permits utilization of the samemachine for boards of varying thickness, including permitting drying ofvery thin flexible circuit boards.

SUMMARY OF THE INVENTION In accordance with the present invention thereis provided a I circuit board drier employing a novel air knife. The airknife itself comprises a cylindrical duct opening longitudinally into ablade portion'formed by a pair of elongate, planar blade members. Theblade members converge to form, adjacent their apex, a narrow elongateorifice or slit having an opening ranging in width from 0.032 to 0.125inch. A deflector lip extends from one edge of the orifice for length ofat least 0.125 inch and at an angle of between 15 and 25 with respect toa normal to the plane of the orifice. When air under pressure is fed tothe interior of the cylindrical duct, it escapes through the orifice,deflected by the deflection lip, to form a thin' blade of air having ananemometer static pressure of at least 10 inches of water. When directedat the surface of a circuit board at an appropriate angle, the air knifeis exceptionally effective in drying the board. Further, the air knifeis considerably quieter than slotted air knife devices of the prior art.

The inventive air knives are incorporated in a drier apparatus utilizinga conveyor formed by a plurality of rotating rollers having their upperedges aligned in a horizontal plane. A second set of rollers, disposedatop the first set and adapted for limited vertical motion, serves thefunction of maintaining the circuit board in a horizontal plane as it isconveyed'past the set of air knives.

In a preferred embodiment, several air knives are situated above theplane of the conveyed circuit board and oriented in an angle of froml0,to 20 with respect to that board surface. These air knives effectdrying of the upper board surface, an appropriate baffle arrangementbeing used to prevent the air from each knife from circulating into thespace associatedv with the next adjacent air knife. A second set of airknives isdisposed beneath the plane of the conveyed circuit boards, andpositioned at an appropriate angle to effectuate drying of the circuitboard bottom. An underlying pan and drain catches residual liquids blownfrom the board as it is'dried.

To permit conveyor drying of very thin circuit boards, the inventivedrier is provided with upper. and lower. sets of guidewires recessedrespectively in grooves in the upper and lower conveyor rollers. Thebetween-wire spacing is selected in accordance with the dimensions ofthe board to be dried. A thin circuit board, when conveyed through thedrier, will be maintained in a horizontal plane between the guidewiresdespite the flexibility of the board and the pressure exerted by the airknives.

Thus, it is an object of the present invention to provide an improvedair knife drying apparatus.

Another object of the present invention is to provide an improvedapparatus for drying circuit boards.

It is another object of the present invention to provide an apparatusfor the conveyor drying of circuit boards of any dimension or thickness.

Yet another object of the present invention is to provide a circuitboard drier capable of drying thin, flexible boards.

It is a further object of the present invention to provide an air knifehaving an elongate slit-type orifice and a deflection lip angularlyextending from one edge of the slit.

A further object of the present invention is to provide a circuit boarddrier utilizing a plurality of horizontally aligned driven rollers toconvey a circuit board past one or more air knives of the typeincorporating an elongate slit and a deflection lip extending from oneedge of the slit.

Still a further object of the present invention is to provide a circuitboard drier incorporating two sets of guidewires disposed to maintain aflexible circuit board in a horizontal planar orientation while passingthrough the drier.

BRIEF DESCRIPTION OF THE DRAWINGS Still other objects, features andattendant advantages of the present invention will become apparent tothose skilled in the art from a reading of the following detaileddescription of the preferred embodiments constructed in accordancetherewith, taken in conjunction with the accompanying drawings whereinlike numerals designate like parts in the several figures and wherein:

FIG. 1 is a perspective view of a preferred embodiment of the inventivecircuit board drier, the view being partially cut away to disclose thecentrifugal blower, duct and air knives employed in the drier.

FIG. 2 is a perspective view of a high velocity air knife in accordancewith the present invention; several such air knives are incorporated inthe circuit board drier illustrated in FIG. 1.

FIG. 3 is a partial sectional view of the inventive circuit board drier,as seen generally along the line 3-3 of FIG. 1. Evident in the FIG. aresix air knives, of the type illustrated in FIG. 2, arranged for dryingboth the top and bottom of a printed circuit board conveyed past the airknives by a plurality of rotating rollers.

FIG. 4 is a partial rear plan view, partly in section, of the inventivecircuit board drier as seen generally along the lines 4-4 of FIG. 1.This view best illustrates the grooved rollers used to accommodate twosets of guidewires useful for directing very thin printed circuit boardsthrough the drier.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings,and particularly to FIG. 1 thereof, it may be seen that the inventivecircuit board drier generally is enclosed in a housing 12 ofconventional metal fabrication. Mounted within housing 12 are a pair ofspaced parallel support members 14a and 14b (support member 14b beinghidden in FIG. 1) between which extend a plurality of lower rollers 16.The axes of rollers 16 all are parallel, and the rollers all are of thesame diameter, their upper edges lying within a common horizontal plane.An appropriate roller drive mechanism, described in detail hereinbelow,imparts rotational motion at a common speed to some or all of rollers16, so that when a printed circuit board 18 is placed upon lower rollers16 adjacent the front of drier 10, as shown in FIG. 1, the circuit boardwill be transported toward the rear of drier l0 atop the rollers.

Still referring to FIG. 1, it may be seen that support members 14a and14b respectively include upwardly projecting portions 14a and 14b,between which extend a plurality of upper rollers 20. As will bedescribed hereinbelow, upper rollers 20 are not driven, and areappropriately mounted to permit their vertical displacement as printedcircuit board 18 passes thereunder. A ventilated hood 22 also issupported by members 14a and 14b, hood 22 enclosing upper rollers 20.

Actual drying of circuit board 18 is accomplished by a plurality ofinventive air knives 24, the upper three of which are evident in FIG. 1.A high speed centrifugal blower 26, powered by motor 27, supplies air athigh velocity through a duct 28 to air knives 24 via the open ends 30thereof. This high velocity air in turn is directed via air knife blade32 toward the printed circuit board 18 being conveyed through the drieratop rollers 16.

Still referring to FIG. 1, circuit board drier 10 is provided withappropriate on and off switches 33a and 3311 which control the supply ofelectricity to blower motor 27 and to the drive system for rollers 16.The apparatus further is provided with a conventional electrical speedcontrol device 330 permitting adjustment of the speed of rotation oflower rollers 16, and hence of the linear rate at which printed circuitboard 18 is conveyed through drier 10.

The configuration of the inventive air knife 24 employed in circuitboard drier 10 most clearly is illustrated in FIG. 2. As seen therein,air knife 24 comprises a cylindrical duct 34 which is open at end 20 andclosed at end 36. An elongate, axial opening 38 permits communicationbetween the interior of cylindrical duct 34 and the interior of airknife blade 32. Blade 32 itself comprises a pair of planar, elongateblade members 40a and 40b extending from adjacent opposite edges ofopening 38 and converging to form an elongate, slotted orifice 42 ofsubstantially constant width. The ends 44 of air knife blade 32 areclosed. An elongate deflection lip 46 extends from one edge of orifice42, forming an obtuse angle with planar blade member 40b.

In a preferred embodiment, the width of orifice 42 is at least 0.030inch but less than 0.125 inch. The angle between planar blade members400 and 40b typically may be on the order of 20. With respect todeflection lip 46, if a radius were drawn from the axis of cylindricalduct 34 through the centerline of elongate orifice 42, the preferredangle between this extended radius and deflection lip 46 is between 25and 35. The length of lip 46 preferably is between one-eighth inch andthreeeighths inch, a length of about 0.25 inch being optimum. Further,the preferred orientation of air knife 24 with respect to the article tobe dried is with this extended radius (i.e. a radius of duct 36 passingthrough the center line of orifice 42) forming an angle of from 10 to 20with respect to the surface of the article to be dried.

With duct end 36 closed, when l ,000 cubic feet per minute of air issupplied to cylindrical duct 34 via open end 30, a knife edge of airhaving an anemometer reading of greater than 10 inches static pressureof water is exhausted via orifice 42. It has been found empirically thatwith the preferred dimensions described, an air knife edge of greaterthan l0 inches static pressure of water accomplishes exceptionallyeffective drying of a surface. Further, due at least in part to theaction of deflector lip 46, the airflow through air knife 24 isremarkably quiet, producing substantially less noise than produced byair knives of the prior art.

The manner in which air knives 24 are incorporated in circuit boarddrier 10 is shown most clearly in FIG. 1 and in the sectional view ofFIG. 3. Referring to these FIGS. it may be seen that drier 10incorporates six air knives 24, three being disposed above lower rollers16 so as to dry the upper surface of circuit board 18. The remainingthree air knives (herein designated 24a) are disposed below the upperedges of lower rollers 16, so as to affect drying of the bottom surfaceof circuit board 18. Lower air knives 24a, although hidden from view inFIG. 1, also interiorally communicate via their open ends 30 with duct28, so that centrifugal blower 26 serves as the high velocity air sourcefor all of the drier air knives.

For optimum drying efficiency, each of air knives 24 and 24a is orientedso that an extended radius drawn from the axis of cylindrical duct 34through the center of orifice 42 intersects the plane defined by theupper edges of lower rollers 16 at an angle of from to 20, with an angleof about being preferred. Note that the resultant airflow over thecircuit boards is toward the front of the drier, i.e., toward thetrailing edge of the board being dried.

As most clearly evident in FIG. 3, a foam rubber 4 48 is provided withinhood 22, the foam rubber being of sufficient thickness so as to abutagainst the upper portions of cylindrical ducts 34 of upper air knives24. Foam rubber 48 serves two functions. First, it acts as a sounddampener, further reducing the low level of noise produced by air knives24. Secondly, foam rubber 48 prevents high velocity air, exhaustedforwardly of a particular air knife 24, from flowing back into theregion in front of the next rearward air knife. It has been foundempirically that significantly improved circuit board drying is achievedby so limiting air communication between the regions associated withadjacent air knives. Of course, this configuration also insures thatliquids blown from the board surface by a particular air knife will notbe splashed back onto portions of the board which have passed that airknife. In an alternative embodiment, foam rubber 48 may be dispensedwith and appropriate baffles 50 (shown in phantom in FIG. 3) may be usedto limit air communication between the regions of adjacent air knives.

An air shield 52 (see FIG. 3) is provided to deflect downward airflowing out of the forward edge of hood 22. Air shield 52 thus preventsthis exhausted air from blowing in the face of an operator who isinserting printed circuit boards into the drier. Also apparent in FIG. 3is a drain pan 54 situated below lower rollers I6 and lower air knives24a so as to collect water or other liquids dripping from circuit board18 as it proceeds through the drier. A drain 56 and an associateddrainpipe 58 are provided to carry away water or other liquidsaccumulating in pan 54.

As best illustrated in FIGS. 3 and 4, each of lower rollers 16 isprovided with a shaft 60 extending through support member 14a andterminating in a sprocket 62. A chain drive engages each of sprockets62, and is driven by a conventional variable speed motor 66 and geardrive 68 (FIG. 3), the speed of which is adjustable by means of control38. Thus, motor 66, transmission 68, chain drive 64 and sprocket 62 allcooperate to rotate lower rollers 16 clockwise as seen in FIG. 3,thereby providing a system for conveying circuit boards through drier10.

Each of upper rollers is adapted to be displaced vertically as printedcircuit board passes beneath it. This is illustrated in FIG. 3, whereinprinted circuit board 18 is shown passing beneath thefirst two upperrollers 20a, each of which has been displaced upward by an amount equalto the thickness of board 18. In contradistinction, the remainder ofupper rollers 20 illustrated in FIG. 3 have not been displaced upward,but are resting in tangential contact with the corresponding ones-oflower rollers 16.

The system permitting vertical displacement of the right end of roller20 best is shown in FIG. 4. Although not shown in FIG. 4, a similararrangement is used at the left end of roller 20. Upper support members140' and 14b each are provided with a plurality of vertically disposedslots 70, corresponding in number to the number of upper rollers 20.Disposed within each slot 70 is a slideable member 72 through whichextends the shaft 74 of upper roller 20. Of course, a conventional ballbearing (not shown) may be employed to mount shaft 74 to member 72.Member 72 itself is free to slide vertically in slot 70, and is biaseddownward by a coil spring 76 extending from a countersunk hole 78 inupper support member 140. This configuration provides an independentfloating mount for each end of upper roller 20, and permits the upwarddisplacement of each roller 20 to accommodate itself to the particularthickness and width of the circuit board being dried.

While upper rollers 20 may be driven rotationally, this has not beenfound necessary forproper functioning of theinventive drier, and theembodiment shown incorporates no driving mechanism for these upperrollers. However, the upper rollers do play the important roll ofpreventing circuit board 18 from being blown upward off of lower rollers16 by the force of the air projecting from lower air knives 240. -Byimparting a downward force, upper rollers 20 maintain circuit board 18substantially horizontal throughout the time that the board is movingthrough drier 10. To prevent damage to the surfaces of circuit board 18,it has been found desirable to fashion each of lower rollers 16 andupper rollers 20 of a tough yet resilient material such as neoprenerubber.

In modern electronic systems it is becoming increasingly common to useexceptionally thin printed circuit boards. Such circuit boards, whichtypically may be on the order of 0.002 inch thick, may be usedindependently or may be laminated with other boards of like thickness toprovide a multilayer circuit board structure. The drying of such thincircuit boards present unique problems in that such boards tend to bendor flex very easily, and would readily be deflected downward or upwardaround rollers 16 or 20 (see FIG. 3) under the force exerted by airknives 24 or 24a. To permit such exceptionally thin circuit boards to bedried by apparatus 10, the present invention incorporates two sets ofguidewires which prevent the curling or vertical displacement of thincircuit boards as they are conveyed through the inventive drier. Thelower set of guidewires 84 is evident in in FIG. I, 3 and 4, while theupper set of guidewires 86 best may be seen in FIGS. 3 and 4.

In embodiments of the inventive circuit board drier 10 incorporatingguidewires, lower guidewires 84 are stretched between a lower forwardguidewire support bar 88 (see FIGS. 1 and 3) and a set of resilientfingers 90 (see FIGS. 3 and 4) equal in number to the number ofguidewires 84. Fingers 90 preferably are of spring steel, each fingerbeing attached at its lower end to a tapered rear support bar 92 bymeans of screw 94.

Similarly, upper guidewires 86 are stretched between an upper forwardguidewire support bar 96, which bar itself is supported between members140' and 14b, and an upper set of resilient fingers 98 equal in numberto the number of guidewires 86. Fingers 98 also are of spring steel,each finger being attached at its upper end to a tapered upper rearsupport bar 100 by means ofa screw 102.

As best shown in FIGS. 1 and 4, those lower rollers 16 spanned byguidewires 84 are grooved to permit the guidewires to rest in ahorizontal plane slightly lower than the plane defined by the topmostedges of rollers 16. Thus, in a typical embodiment the diameter ofguidewires 84 may be on the order of from 0.020 inch to 0.045 inch,while grooves 104 typically may be 0.25 inch wide and have a depth onthe order of 0.075 inch. With this configuration the top edges ofrollers 16 will project slightly above the level of lower guidewires 84,as is apparent in FIG. 3. This permits sufficient contact between theupwardly projecting edges of rollers 16 and the lower surface of circuitboard 18 so as to convey the circuit board through the drier. The springaction of fingers tends to keep wires 84 taut within the grooves 104 ofrollers 16.

In a similar manner, those upper rollers 20 spanned by upper guidewires86 are provided with a like set of grooves 106. While the wire size forupper guidewires 86 also typically is on the order of from 0.020 inch0.045 inch, the depth of grooves 106 will depend on the anticipatedthickness of the boards to be dried by apparatus 10. Where onlyrelatively thin boards are to be dried, grooves 106 typically may be onthe order of 0.25 inch wide and 0.075 inch deep. However, where it isanticipated that drier 10 also will be used to dry circuit boards ofgreater thickness, grooves 106 may be as deep as 0.30 inch. In eitherinstance, fingers 98 are sufficiently resilient to keep upper guidewires86 taut within grooves 106 regardless of the thickness of the boardbeing conveyed through the drier.

It will be appreciated that although the circuit board drier illustratedin FIGS. 1, 3 and 4 includes upper and lower guidewires, such guidewiresare not required, and may be omitted completely from embodiments of theinvention which are not to be used for drying very thin, flexiblecircuit boards. On the other hand, in those embodiments incorporatingsuch upper and lower guidewires, the drier may be used for drying verythin flexible boards and for drying thicker, substantially rigid boards.When thin, flexible boards are dried, the boards will be guided throughthe drier by wires 84 and 86, these wires preventing the board fromcurling upward or downward as a result of the air pressure from airknives 24 and 24a. When a rigid circuit board is conveyed through drier10, the guidewires will not interfere with passage of the board betweenair knives 24, the depth of grooves 106, and the springiness of fingers98 cooperating to allow upper wires 86 to be displaced upwardsufi'rciently to allow passage of a board which may be much thicker thanthe minimum distance between the upper and lower guidewires.

While circuit board drier 10 herein has been illustrated as employingsix air knives, this is not required, and fewer or more air knives maybe employed. Similarly, other embodiments may utilize air knives onlyabove, or only below the object being dried, and not both above andbelow as illustrated in the embodiment shown in the drawings. Moreover,while the invention has been described in terms of its application fordrying printed circuit boards, the invention is by no means so limited,and the apparatus could be employed for drying articles of any variety.Nor need such articles be limited to those which are generally flat inshape, the inventive air knife configuration of FIG. 2 being useful forproviding an effective, quite, high velocity flow of air for dryingobjects of any shape.

While the invention has been described with respect to several physicalembodiments constructed in accordance therewith, it will be apparent tothose skilled in the art that various modifications and improvements maybe made without departing from the scope and spirit of the invention.Accordingly, it is to be understood that the invention is not to belimited by the specific illustrative embodiments, buy only by the scopeof the appended claims.

lclaim:

1. An air knife adapted for drying an article, and characterized by abody, the cross-sectional area of which converges to a slitlike orifice,comprising a cylindrical duct having a longitudinally extending openingtherein, and a pair of elongate planar blade members extending fromopposite edges of said opening and converging to form said slitlikeorifice adjacent their apex, and a deflector lip extending from one edgeof said blade member at an angle thereto.

2. An air knife as defined in claim 1 wherein the length of saiddeflector lip is at least one-eighth inch.

3. An apparatus for drying a circuit board, said apparatus comprising:

at least one air knife of the type defined in claim 1; and

conveyor means for transporting said circuit board past said 4. Anapparatus as defined in claim 3 wherein said air knife is oriented sothat a radius extending from the axis of said cylindrical duct throughthe center of said orifice intersects the surface of said transportedcircuit board at an angle of from 10 to 5. An apparatus as defined inclaim 4, and comprising a plurality of said air knives, at least one ofsaid air knives being directed toward the top surface of saidtransported circuit board, at least one other of said air knives beingdirected toward the bottom surface of said transported circuit board.

6. An apparatus as defined in claim 5 further comprising means forexhausting air through the orifices of each of said air knives at a ratesufficient to produce an air knife edge having a static pressure of atleast 10 inches of water.

7. An apparatus as defined in claim 6 where said conveyor meanscomprises a first set of rollers having their upper edges disposed in afirst horizontal plane, and means for rotating said rollers.

8. An apparatus as defined in claim 7 wherein said conveyor meansfurther comprises a second set of rollers having their lower edgesdisposed in a second horizontal plane above said first horizontal plane,each roller of said second set being adapted to be displaced verticallyas said circuit board is transported therebeneath.

9. A device for conveying a thin flexible circuit board past a drier,said device comprising:

a first set of rollers having their upper edges disposed in a firsthorizontal plane, each roller of said first set having pluralcircumferential grooves therein;

means for rotating said first set of rollers;

a first plurality of guidewires aligned perpendicular to the axes of,and disposed within the grooves of said first set of rollers;

a second set of rollers having their lower edges disposed in a secondhorizontal plane disposed immediately above said first horizontal plane,each roller of said second set being adapted independently to bedisplaced vertically as said circuit board is conveyed thereunder, eachroller of said second set having plural circumferential grooves therein;and

a second plurality of guidewires aligned perpendicular to the axes of,and disposed within the grooves of said second set of rollers.

10. A device as defined in claim 9 wherein said drier comprises one ormore air knives each characterized by a body the cross-sectional area ofwhich converges to a slitlike orifice and a deflector lip extending fromone edge of said orifice at an acute angle with respect to a normal tothe plane of said orifice.

11. An apparatus as defined in claim 6 wherein said conveyor meanscomprises:

a first set of rollers having their upper edges disposed in a firsthorizontal plane, each roller of said first set having pluralcircumferential grooves therein;

means for rotating said first set of rollers;

a first plurality of guidewires aligned perpendicular to the axes of,and disposed within the grooves of said first set of rollers;

a second set of rollers having their lower edges disposed in a secondhorizontal plane disposed immediately above said first horizontal plane,each roller of said second set being adapted independently to bedisplaced vertically as said circuit board is conveyed thereunder, eachroller of said second set having plural circumferential grooves therein;and

a second plurality of guidewires aligned perpendicular to the axes of,and disposed within the grooved of said second set of rollers.

1. An air knife adapted for drying an article, and characterized by abody, the cross-sectional area of which converges to a slitlike orifice,comprising a cylindrical duct having a longitudinally extending openingtherein, and a pair of elongate planar blade members extending fromopposite edges of said opening and converging to form said slitlikeorifice adjacent their apex, and a deflector lip extending from one edgeof said blade member at an angle thereto.
 2. An air knife as defined inclaim 1 wherein the length of said deflector lip is at least one-eighthinch.
 3. An apparatus for drying a circuit board, said apparatuscomprising: at least one air knife of the type defined in claim 1; andconveyor means for transporting said circuit board past said orifice. 4.An apparatus as defined in claim 3 wherein said air knife is oriented sothat a radius extending from the axis of said cylindrical duct throughthe center of said orifice intersects the surface of said transportedcircuit board at an angle of from 10* to 20*.
 5. An apparatus as definedin claim 4, and comprising a plurality of said air knives, at least oneof said air knives being directed toward the top surface of saidtransported circuit board, at least one other of said air knives beingdirected toward the bottom surface of said transported circuit board. 6.An apparatus as defined in claim 5 further comprising means forexhausting air through the orifices of each of said air knives at a ratesufficient to produce an air knife edge having a static pressure of atleast 10 inches of water.
 7. An apparatus as defined in claim 6 wheresaid conveyor means comprises a first set of rollers having their upperedges disposed in a first horizontal plane, and means for rotating saidrollers.
 8. An apparatus as defined in claim 7 wherein said conveyormeans further comprises a second set of rollers having their lower edgesdisposed in a second horizontal plane above said first horizontal plane,each roller of said second set being adapted to be displaced verticallyas said circuit board is transported therebeneath.
 9. A device forconveying a thin flexible circuit board past a drier, said devicecomprising: a first set of rollers having their upper edges disposed ina first horizontal plane, each roller of said first set having pluralcircumferential grooves therein; means for rotating said first set ofrollers; a first plurality of guidewires aligned perpendicular to theaxes of, and disposed within the grooves of said first set of rolleRs; asecond set of rollers having their lower edges disposed in a secondhorizontal plane disposed immediately above said first horizontal plane,each roller of said second set being adapted independently to bedisplaced vertically as said circuit board is conveyed thereunder, eachroller of said second set having plural circumferential grooves therein;and a second plurality of guidewires aligned perpendicular to the axesof, and disposed within the grooves of said second set of rollers.
 10. Adevice as defined in claim 9 wherein said drier comprises one or moreair knives each characterized by a body the cross-sectional area ofwhich converges to a slitlike orifice and a deflector lip extending fromone edge of said orifice at an acute angle with respect to a normal tothe plane of said orifice.
 11. An apparatus as defined in claim 6wherein said conveyor means comprises: a first set of rollers havingtheir upper edges disposed in a first horizontal plane, each roller ofsaid first set having plural circumferential grooves therein; means forrotating said first set of rollers; a first plurality of guidewiresaligned perpendicular to the axes of, and disposed within the grooves ofsaid first set of rollers; a second set of rollers having their loweredges disposed in a second horizontal plane disposed immediately abovesaid first horizontal plane, each roller of said second set beingadapted independently to be displaced vertically as said circuit boardis conveyed thereunder, each roller of said second set having pluralcircumferential grooves therein; and a second plurality of guidewiresaligned perpendicular to the axes of, and disposed within the grooved ofsaid second set of rollers.